1. Field of the Invention
The invention relates to a method of making optical devices that guide light, and in particular that incorporate two dimensional photonic crystals for confinement of light.
2. Description of the Prior Art
High reflectivity mirrors have been a key ingredient to reducing the modal volume of optical laser cavities. In 1991, the operation of ultra-small cavities with lateral dimensions of 400 nm diameters was realized. The mode volume in these lasers was still rather large, approximately two cubic wavelengths due to the deep penetration of light into the mirrors.
Microdisk lasers with similar mode volumes emerged in 1993 and relied on high cavity Qs resulting from total internal reflection of light from the perimeter of the disk. In these devices, the light is guided in a thin slab, and reflects as whispering gallery modes along the circumference of the circular laser cavity. Consequently, bend losses become prohibitively large in devices with diameters below 1.5 microns.
What is needed is a design and fabrication technique by which one can fabricate nanocavities in room temperature devices.
The invention is defined as a method of fabricating a semiconductor membrane having a two dimensional, photonic, crystal semiconductor device defined therein comprising the steps of disposing or defining the thickness of a semiconductor membrane or layer on a lower index substrate and patterning the semiconductor membrane with a pattern of vertical holes disposed or etched therethrough, and undercutting the semiconductor membrane or positioning the semiconductor layer onto the low refractive index substrate. The pattern of holes define a region of the semiconductor layer, which is the two dimensional photonic crystalline semiconductor device. A membrane is formed in which the semiconductor layer laterally at least partially confines light by the pattern of holes and which vertically at least partially confines light by total internal reflection.
In one embodiment the step of forming the membrane comprises undercutting the semiconductor layer to define a waveguiding membrane. In another embodiment the step of forming the membrane comprises epitaxially lifting the semiconductor layer off the substrate and disposing the semiconductor layer between two layers of other materials having a lower index of refraction than the semiconductor layer to define the waveguiding membrane. In one embodiment the step of disposing the semiconductor layer between two layers of other materials to define the waveguiding membrane comprises disposing the semiconductor layer between two layers of glass.
The step of disposing or defining the thickness of the semiconductor layer comprises disposing the semiconductor layer on a silicon on insulator (SOI) substrate, or more specifically oxidizing the silicon membrane and removing the formed SiO2 layer using HF acid. For example, the semiconductor layer is disposed on a Si layer on a SiO2 clad Si substrate, or alternatively on a GaAs layer on an AlAs clad GaAs substrate.
The step of patterning the semiconductor layer comprises patterning the mask on the semiconductor layer by means of electron beam lithography and patterning the semiconductor layer by means of chemically assisted ion beam etching or any other type of wet or dry etching technique.
Although the method of the invention has been described as steps, it is to be expressly understood that the methodology is generally defined by the claims and is not limited to the disclosed specification under the construction of 35 USC 112. The invention further comprises a membrane and semiconductor devices made from membranes. The invention can be better visualized by turning to the following drawings wherein like elements are referenced by like numerals.